My black water sprung a leak at the gate valve. I removed the tank floor and found a 2 inch piece of 2 inch pvc pipe between the tank bottom and insulation.
My question is whether the pvc piece is needed? Maybe it creates an air gap for insulation? The tank is sagging quite a bit.
I plan to use some angle steel to brace up tank.

My guess would be is that piece of pipe is scrap that was cut from a vent or drain somewhere, once anything drops during construction NO ONE picks it up, I've gathered probably a quart jar full of all types of screws, wire stripping, sawdust & wood cut outs & still, after nearly 5 years of travel, have sawdust falling from various light fixtures.